Imagery is the pictorial or graphical representation of a subject by sensing quantitatively the patterns of electromagnetic radiation emitted by, reflected from, or transmitted through a scene of interest. Basically there are two types of imagery, chemical and electronic.
Chemical imagery or traditional photography relies on the interaction between exposing light from a scene on a photosensitive material in such a manner as ultimately to render visible an image of the incident light exposure distribution. The interaction is between the individual exposure photons of light and the photosensitive elements of the photosensitive material. The resulting image is composed of microscopic picture elements corresponding in position to those photosensitive elements that have received adequate exposure.
Electronic imagery utilizes the sensitivity of various electronic sensors to different bands of the electromagnetic spectrum. The energy received by the sensors is transduced into an electronic signal or electrical effect so that the signal or effect may be processed to display the sensed information. The most common forms of electronic imagery are: television cameras, electronic still cameras, and charge coupled devices, etc. The raw information that makes up the electronic image is in the form of pixels. In a digitized picture a pixel is one of the dots or resolution elements making up the picture.
A picture is not always a satisfactory representation of the original object or scene. The picture may have a poorly chosen gray scale, i.e., it may be overexposed or underexposed. The picture may also be geometrically distorted, or the picture may be blurred or noisy. Image enhancement is the process by which a scene, or one or more portions of a scene, are enhanced so that the scene has more detail or that the scene is more visually appealing and/or contain additional information. The foregoing process is often used to increase the usefulness of microscopy pictures, satellite pictures or reconnaissance pictures. Image enhancement involves the reworking of the raw data after the data has been received. Electronic manipulation of the received data can increase or decrease emphasis, extract data selectively from the total received data, and examine data characteristics that would not show up by normal imagery.
The pixels can be measured one at a time at a rapid rate of speed for brightness and other quantities and over a wide scale of selections. For example, black may equal zero, medium gray may equal 128, and white may equal 255 so that groupings of input information can be made to provide better contrast in pattern and blackness, when the information is regrouped and reassembled for display. Computers have been utilized to process the pixels and enhance the image.
One of the methods utilized by the prior art to enhance images was contrast enhancement. Contrast enhancement transformed every pixel in the image by a continuous or discontinuous function into a new enhanced image. This caused the stetching or compression of contrast of the image.
Another method utilized by the prior art to enhance images was histogram transformation. The histogram transformation constructed a transfer function from the raw gray scale image to the enhanced image.
One of the disadvantages of the contrast enhancement and histogram transformation methods was that the aforementioned methods required computations for every pixel in the gray scale image. Thus, for normal images, e.g., 512 pixels by 480 pixels a large amount of computations are required. This necessitated the use of expensive custom hardware in order to obtain high computation speeds.
Another disadvantage of the prior art is that most image enhancement techniques do not supply feedback to inform the user of the system that different enhancement results may be obtained under different imaging conditions.
An additional disadvantage of the prior art was that some image enhancement techniques do not allow the user to choose gray scale values over different regions of the image.